Pattern and Amount of Change of Upper Front Teeth After Retention with a Bonded Retainer 2010 G

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Pattern and amount of change of upper front teeth Pattern and amount of change of upper front teeth after retention with a bonded retainer after retention with a bonded retainer Follow-up one to seven years postretention Follow-up one to seven years postretention

Sasan Naraghi Sasan Naraghi

Department of Orthodontics Department of Orthodontics Institute of Odontology at the Sahlgrenska Academy Institute of Odontology at the Sahlgrenska Academy University of Gothenburg University of Gothenburg 2010 2010

To my beloved family Peggy, Jasmin and Shirin To my beloved family Peggy, Jasmin and Shirin

To my dear brother Sirus who has been my leading star To my dear brother Sirus who has been my leading star and a source of inspiration in my life and a source of inspiration in my life

ISBN 978-91-633-7846-1 ISBN 978-91-633-7846-1

Printed by Intellecta Infolog AB, Göteborg 2010 Printed by Intellecta Infolog AB, Göteborg 2010

CONTENTS CONTENTS

PREFACE 7 PREFACE 7

ABSTRACT 8 ABSTRACT 8

POPULÄRVETENSKAPLIG SAMMANFATTNING 10 POPULÄRVETENSKAPLIG SAMMANFATTNING 10

INTRODUCTION 12 INTRODUCTION 12

AIMS 23 AIMS 23

MATERIALS AND METHODS 24 MATERIALS AND METHODS 24

RESULTS 30 RESULTS 30

DISCUSSION 33 DISCUSSION 33

CONCLUSIONS 38 CONCLUSIONS 38

ACKNOWLEDGMENTS 39 ACKNOWLEDGMENTS 39

REFERENCES 40 REFERENCES 40

PAPER I 47 PAPER I 47

PAPER II 57 PAPER II 57

PREFACE PREFACE

This thesis is based on the following two papers, which are referred to as This thesis is based on the following two papers, which are referred to as paper I and paper II. paper I and paper II.

Paper I. Naraghi S, Andrén A, Kjellberg H, Mohlin B. Relapse tendency Paper I. Naraghi S, Andrén A, Kjellberg H, Mohlin B. Relapse tendency after orthodontic correction of upper front teeth retained with a bonded after orthodontic correction of upper front teeth retained with a bonded retainer. Angle Orthod. 2005;76: 570–576. retainer. Angle Orthod. 2005;76: 570–576.

Paper II. Andrén A, Naraghi S, Mohlin B, Kjellberg H. Pattern and Paper II. Andrén A, Naraghi S, Mohlin B, Kjellberg H. Pattern and amount of change after orthodontic correction of upper front teeth 7 years amount of change after orthodontic correction of upper front teeth 7 years postretention. Angle Orthod. 2010;80:620–625. postretention. Angle Orthod. 2010;80:620–625.

These papers are reprinted with the kind permission from the copyright These papers are reprinted with the kind permission from the copyright holder, Angle Orthodontist. holder, Angle Orthodontist.

7 7 ABSTRACT ABSTRACT

Objectives: Objectives: To investigate the amount and pattern of relapse of maxillary front teeth To investigate the amount and pattern of relapse of maxillary front teeth previously retained with a bonded retainer for two to four years. Which previously retained with a bonded retainer for two to four years. Which teeth are more prone to relapse? Is there any difference in behavior teeth are more prone to relapse? Is there any difference in behavior between contact point displacement and rotation? What is the magnitude of between contact point displacement and rotation? What is the magnitude of the relapse in short-term and long-term? the relapse in short-term and long-term?

Materials and Methods: Materials and Methods: The study group originally consisted of 45 patients, and 27 patients on The study group originally consisted of 45 patients, and 27 patients on recall for the second study. Recordings from study models before treatment recall for the second study. Recordings from study models before treatment (T1), at debonding (T2), one year after removal of the retainer (T3) and (T1), at debonding (T2), one year after removal of the retainer (T3) and seven years postretention (T4) were present. All patients had been treated seven years postretention (T4) were present. All patients had been treated with fixed edgewise appliances by the same operator. The irregularity with fixed edgewise appliances by the same operator. The irregularity index (sum of contact point displacement [CPD]), and rotations of front index (sum of contact point displacement [CPD]), and rotations of front teeth in relation to the Raphe line and intercanine distance, were calculated teeth in relation to the Raphe line and intercanine distance, were calculated at T1, T2, T3 and T4. at T1, T2, T3 and T4.

Statistical analysis: Statistical analysis: Paired t-test, Pearson’s product-moment correlation and Pearson’s product- Paired t-test, Pearson’s product-moment correlation and Pearson’s product- moment correlation coefficient were applied. For all statistical analyses, the moment correlation coefficient were applied. For all statistical analyses, the statistical significance level was set to 5%. statistical significance level was set to 5%.

Results: Results: Before treatment (T1), the mean irregularity index was 10.1 (range 3.0– Before treatment (T1), the mean irregularity index was 10.1 (range 3.0– 29.9). The largest displacements were recorded between laterals and 29.9). The largest displacements were recorded between laterals and centrals followed by the displacement between laterals and canines. The centrals followed by the displacement between laterals and canines. The smallest deviations were found between the centrals. smallest deviations were found between the centrals. After treatment (T2), the mean irregularity index was 0.7 (range 0.0–2.1). After treatment (T2), the mean irregularity index was 0.7 (range 0.0–2.1). There was a significant difference in the index between T1 and T2 (P There was a significant difference in the index between T1 and T2 (P <.0001). <.0001). One year postretention (T3), the mean irregularity index was 1.4 (range 0– One year postretention (T3), the mean irregularity index was 1.4 (range 0– 5.1). There was a significant difference in the index between T2 and T3 (P 5.1). There was a significant difference in the index between T2 and T3 (P <.0001). <.0001). Results from the second study showed that there were no statistically Results from the second study showed that there were no statistically significant differences between the change in mean CPDs for the contacts significant differences between the change in mean CPDs for the contacts canines/laterals, laterals/centrals, or centrals/centrals. The mean irregularity canines/laterals, laterals/centrals, or centrals/centrals. The mean irregularity

8 8 index for the 27 patients examined in the second study was 10.3 (range 3.7- index for the 27 patients examined in the second study was 10.3 (range 3.7- 29.9) at T1, 0.9 (range 0.0-2.1) at T2, 1.3 (range 0.0-3.5) at T3 and 2.0 29.9) at T1, 0.9 (range 0.0-2.1) at T2, 1.3 (range 0.0-3.5) at T3 and 2.0 (range 0.0-5.8) at T4. (range 0.0-5.8) at T4. No correlations were found between the pretreatment and postretention No correlations were found between the pretreatment and postretention irregularity T1/T3 and T1/T4. There was a significant association between irregularity T1/T3 and T1/T4. There was a significant association between the irregularity index at T3 and T4 (R = 0.938, P < .0001). the irregularity index at T3 and T4 (R = 0.938, P < .0001). The irregularity index of the maxillary front teeth changed very little or not The irregularity index of the maxillary front teeth changed very little or not at all during the first year postretention. Further changes long-term resulted at all during the first year postretention. Further changes long-term resulted in an irregularity index of mean 2.0 mm (range 0.0 – 5.8). The contact in an irregularity index of mean 2.0 mm (range 0.0 – 5.8). The contact relationship between the laterals and centrals seems to be the most critical. relationship between the laterals and centrals seems to be the most critical. Forty rotated teeth in 21 patients were corrected more than 20 o. Mean Forty rotated teeth in 21 patients were corrected more than 20 o. Mean relapse during the first year postretention was 6.7 degrees (range 0.0-14.7). relapse during the first year postretention was 6.7 degrees (range 0.0-14.7). Mean changes during seven years were 8.2 degrees (range 0.0-19.3). Mean changes during seven years were 8.2 degrees (range 0.0-19.3).

Conclusions: Conclusions: • Minor or no relapse in short-term follow-up (one year) was noted in the • Minor or no relapse in short-term follow-up (one year) was noted in the maxillary front after correction of irregularity and a two to four year maxillary front after correction of irregularity and a two to four year period of bonded retention. Further, small relapses occurred long-term period of bonded retention. Further, small relapses occurred long-term i.e. at mean seven years postretention. i.e. at mean seven years postretention. • No significant relation was found between the amount of correction of • No significant relation was found between the amount of correction of contact point displacement and magnitude of relapse neither in one nor contact point displacement and magnitude of relapse neither in one nor seven years postretention. seven years postretention. • There was a strong correlation between irregularity one and seven years • There was a strong correlation between irregularity one and seven years postretention. Stable cases one year postretention are stable in the long- postretention. Stable cases one year postretention are stable in the long- term and cases with small changes one year postretention tend to term and cases with small changes one year postretention tend to deteriorate with time. deteriorate with time. • Most of the rotational relapse was seen one year postretention with • Most of the rotational relapse was seen one year postretention with small changes long-term. small changes long-term. • There was a significant positive correlation between the amount of • There was a significant positive correlation between the amount of correction of incisor rotation and the magnitude of relapse. correction of incisor rotation and the magnitude of relapse. • Of the over corrected contacts, only 50 percent returned to perfect • Of the over corrected contacts, only 50 percent returned to perfect alignment. alignment. • Laterals are more prone to relapse. If, after a three year period of • Laterals are more prone to relapse. If, after a three year period of retention, a decision is made to use permanent retention of the maxillary retention, a decision is made to use permanent retention of the maxillary front teeth, a retainer bonded to only the incisors seems to be a relevant front teeth, a retainer bonded to only the incisors seems to be a relevant choice. choice.

KEY WORDS: KEY WORDS: Retention; Rotation; Relapse; Irregularity; Incisors; Long-term Retention; Rotation; Relapse; Irregularity; Incisors; Long-term

9 9 POPULÄRVETENSKAPLIG POPULÄRVETENSKAPLIG SAMMANFATTNING SAMMANFATTNING

Efter en tandregleringsbehandling, måste tänderna fixeras för att de inte ska Efter en tandregleringsbehandling, måste tänderna fixeras för att de inte ska gå tillbaka mot sina ursprungspositioner. När detta sker säger man att gå tillbaka mot sina ursprungspositioner. När detta sker säger man att tänderna har gått i recidiv (tillbakagång) eller att de har recidiverat. För att tänderna har gått i recidiv (tillbakagång) eller att de har recidiverat. För att undvika recidiv efter ortodontisk behandling limmas en så kallad undvika recidiv efter ortodontisk behandling limmas en så kallad retentionstråd bakom sex framtänder för att hålla kvar tänderna i deras nya retentionstråd bakom sex framtänder för att hålla kvar tänderna i deras nya position tills vävnaden runtom stabiliserats. Tråden får oftast sitta kvar i ca position tills vävnaden runtom stabiliserats. Tråden får oftast sitta kvar i ca 3 år. Det har tidigare varit vanligast att använda retentionstråd i underkäke 3 år. Det har tidigare varit vanligast att använda retentionstråd i underkäke men på senare år används det i allt större utsträckning även i överkäken. men på senare år används det i allt större utsträckning även i överkäken.

Syftet med denna studie var att undersöka storleken på recidivet efter Syftet med denna studie var att undersöka storleken på recidivet efter ortodontisk korrektion av överkäkens framtänder efter att de har varit ortodontisk korrektion av överkäkens framtänder efter att de har varit fixerade under ca 3 år med en retentionstråd. Vilka av de sex framtänderna fixerade under ca 3 år med en retentionstråd. Vilka av de sex framtänderna är mest benägna att gå tillbaka till ursprungsläget? Är det skillnad i recidiv är mest benägna att gå tillbaka till ursprungsläget? Är det skillnad i recidiv mellan kontaktpunktsförskjutningar (avståndet mellan två granntänders mellan kontaktpunktsförskjutningar (avståndet mellan två granntänders kontakt) och rotationer? Finns det skillnader i recidiv på kort och lång sikt? kontakt) och rotationer? Finns det skillnader i recidiv på kort och lång sikt? Studien gjordes på avgjutningar av patienters tänder som framställts i gips Studien gjordes på avgjutningar av patienters tänder som framställts i gips (studiemodeller). Kontaktpunktsförskjutningarna mellan de sex fram- (studiemodeller). Kontaktpunktsförskjutningarna mellan de sex fram- tänderna mättes med hjälp av ett digitalt skjutmått. Modellerna skannades tänderna mättes med hjälp av ett digitalt skjutmått. Modellerna skannades och rotationer av överkäkständerna från hörntand till hörntand, mättes mot och rotationer av överkäkständerna från hörntand till hörntand, mättes mot gommens medellinje (Raphe) som referenslinje. Värdena jämfördes med gommens medellinje (Raphe) som referenslinje. Värdena jämfördes med situationen före behandling (T1), direkt efter behandling (T2) samt ett år situationen före behandling (T1), direkt efter behandling (T2) samt ett år (T3) och sju år (T4) efter det att retentionstråden hade tagits bort. (T3) och sju år (T4) efter det att retentionstråden hade tagits bort.

Resultaten visade att kontaktpunktsförskjutningarna mellan granntänder Resultaten visade att kontaktpunktsförskjutningarna mellan granntänder minskade och framtänderna upplinjerades av den ortodontiska behand- minskade och framtänderna upplinjerades av den ortodontiska behand- lingen (T2). Ett år efter att retentionen tagits bort (T3), hade små men lingen (T2). Ett år efter att retentionen tagits bort (T3), hade små men signifikanta förändringar skett mellan tandkontakterna. Särskilt signifikanta förändringar skett mellan tandkontakterna. Särskilt förändringsbenägna var 2:or (laterala incisiver), därefter 1:or (centrala förändringsbenägna var 2:or (laterala incisiver), därefter 1:or (centrala incisiver) och minst förändringsbenägna var 3:or (hörntänder). incisiver) och minst förändringsbenägna var 3:or (hörntänder). Förändringarna var högst individuella och det skilde sig mycket mellan Förändringarna var högst individuella och det skilde sig mycket mellan olika individer. Vissa individer var mer utsatta för recidiv. olika individer. Vissa individer var mer utsatta för recidiv.

Vid överbehandlingar av vissa tandkontakter (kompensatoriska över- Vid överbehandlingar av vissa tandkontakter (kompensatoriska över- korrigeringar), gick inte alla tänder tillbaka till önskat läge. Hälften av korrigeringar), gick inte alla tänder tillbaka till önskat läge. Hälften av överkorrigeringarna kvarstod och vissa blev till och med sämre. De överkorrigeringarna kvarstod och vissa blev till och med sämre. De tandkontakter som redan vid andra undersökningstillfället (T3) hade börjat tandkontakter som redan vid andra undersökningstillfället (T3) hade börjat recidivera, förvärrades ytterligare vid långtidsuppföljningen (T4). Mönstret recidivera, förvärrades ytterligare vid långtidsuppföljningen (T4). Mönstret

10 10 som beskrivits ovan, att lateraler var mest förändringsbenägna och hörn- som beskrivits ovan, att lateraler var mest förändringsbenägna och hörn- tänder mest stabila, kvarstod på långt sikt. tänder mest stabila, kvarstod på långt sikt.

Slutsatser: Slutsatser: • Mindre recidiv sågs ett år efter retentionens avlägsnande (T3), och • Mindre recidiv sågs ett år efter retentionens avlägsnande (T3), och förvärrades ytterligare något under långtidsuppföljningen (T4), dock i förvärrades ytterligare något under långtidsuppföljningen (T4), dock i mindre omfattning. mindre omfattning. • Det fanns inget samband mellan hur mycket tänderna hade blivit • Det fanns inget samband mellan hur mycket tänderna hade blivit korrigerade och graden av recidiv. korrigerade och graden av recidiv. • Det fanns ett starkt samband mellan recidiv ett och sju år efter • Det fanns ett starkt samband mellan recidiv ett och sju år efter borttagning av retentionen. borttagning av retentionen. • Rotationer var mer benägna att gå tillbaka mot ursprungsläget. • Rotationer var mer benägna att gå tillbaka mot ursprungsläget. • Kontaktrelationen mellan lateraler och centraler är mest recidivbenägna • Kontaktrelationen mellan lateraler och centraler är mest recidivbenägna och hörntänderna är mest stabila. Om man vill behålla retentionen efter och hörntänderna är mest stabila. Om man vill behålla retentionen efter 3 år, räcker det enligt denna studie med att ha kvar den mellan 12-22. 3 år, räcker det enligt denna studie med att ha kvar den mellan 12-22. • Överkorrektioner bör göras med försiktighet då risk finns att tänderna • Överkorrektioner bör göras med försiktighet då risk finns att tänderna inte spontant går tillbaka till önskad position. inte spontant går tillbaka till önskad position.

11 11 INTRODUCTION INTRODUCTION

The goal of orthodontic treatment is to produce a normal or so-called ideal The goal of orthodontic treatment is to produce a normal or so-called ideal occlusion that is morphologically stable and esthetically and functionally occlusion that is morphologically stable and esthetically and functionally well-adjusted. The associations between ideal occlusion, oral health, well-adjusted. The associations between ideal occlusion, oral health, function and esthetics, however, are still in many aspects unclear. function and esthetics, however, are still in many aspects unclear. Orthodontic treatment in the primary and mixed dentition periods mainly Orthodontic treatment in the primary and mixed dentition periods mainly tends to eliminate factors which may have a negative effect on occlusal tends to eliminate factors which may have a negative effect on occlusal development (interceptive orthodontic treatment). Another aim for development (interceptive orthodontic treatment). Another aim for treatment at an early age is to prevent tooth damage by reducing a large treatment at an early age is to prevent tooth damage by reducing a large overjet or correcting ectopic eruption of maxillary canines in individuals, overjet or correcting ectopic eruption of maxillary canines in individuals, where an increased risk for root resorption is suspected. In certain where an increased risk for root resorption is suspected. In certain situations, early treatment is motivated for cost benefit reasons. Examples situations, early treatment is motivated for cost benefit reasons. Examples are congenitally missing teeth and vertically unstable occlusions such as are congenitally missing teeth and vertically unstable occlusions such as Angle class II:2. Angle class II:2. Corrective orthodontic treatments are usually carried out in the permanent Corrective orthodontic treatments are usually carried out in the permanent dentition (adolescents and adults). An ideal occlusion is supposed to go dentition (adolescents and adults). An ideal occlusion is supposed to go hand in hand with optimal oral function and health and, not in the least, hand in hand with optimal oral function and health and, not in the least, acceptable esthetics. There is, however, limited evidence supporting the acceptable esthetics. There is, however, limited evidence supporting the belief that an ideal occlusion improves chewing ability and speech and belief that an ideal occlusion improves chewing ability and speech and reduces the risk for development of TMD (temporomandibular disorders). reduces the risk for development of TMD (temporomandibular disorders). Neither has there been shown significant correlations to caries and Neither has there been shown significant correlations to caries and periodontitis.1,2 periodontitis.1,2 Studies have shown that esthetics, no doubt, is the major motivating factor Studies have shown that esthetics, no doubt, is the major motivating factor for orthodontic treatment both in adults and adolescents. Trulsson et al.3 for orthodontic treatment both in adults and adolescents. Trulsson et al.3 found, in a qualitative study of teenagers on a waiting list for orthodontic found, in a qualitative study of teenagers on a waiting list for orthodontic treatment, that the treatment decision was forced on the individual. Factors treatment, that the treatment decision was forced on the individual. Factors

12 12 like being as others, influence from media and not in the least from dentists like being as others, influence from media and not in the least from dentists were important. Shaw4 reported that visible (frontal) tooth irregularities were important. Shaw4 reported that visible (frontal) tooth irregularities were the most important treatment motivating conditions. were the most important treatment motivating conditions. Even if the concern for esthetics seems to be greatest in young individuals, Even if the concern for esthetics seems to be greatest in young individuals, there is a considerable concern for esthetics in older subjects.5-10 These there is a considerable concern for esthetics in older subjects.5-10 These studies show that patients are interested in well-aligned front teeth and do studies show that patients are interested in well-aligned front teeth and do not care so much about malocclusions in molar areas. Therefore, from the not care so much about malocclusions in molar areas. Therefore, from the patient’s point of view, esthetics and stability of the upper front teeth after patient’s point of view, esthetics and stability of the upper front teeth after treatment is of considerable importance.7,11 Young individuals show more treatment is of considerable importance.7,11 Young individuals show more of their upper front teeth, but with aging, show less due to the lengthening of their upper front teeth, but with aging, show less due to the lengthening of the nose and upper lip covering more of the upper front teeth. Instead, of the nose and upper lip covering more of the upper front teeth. Instead, they may show even more of the lower incisors.12 After the orthodontic they may show even more of the lower incisors.12 After the orthodontic treatment and retention period, when relapses may occur, it is mainly the treatment and retention period, when relapses may occur, it is mainly the front teeth irregularity that causes a lack of satisfaction and calls for new front teeth irregularity that causes a lack of satisfaction and calls for new treatment.3,4,10 treatment.3,4,10 Recent studies indicate that malposition of front teeth may contribute to Recent studies indicate that malposition of front teeth may contribute to low self-esteem and a general feeling of dissatisfaction.3,7,11,13 On the other low self-esteem and a general feeling of dissatisfaction.3,7,11,13 On the other hand, visible malocclusions do not seem to cause psychological illness.14-16 hand, visible malocclusions do not seem to cause psychological illness.14-16 Orthodontists, in general, are facing two challenges; the first is the Orthodontists, in general, are facing two challenges; the first is the treatment and alignment of the dental arches and the second is maintenance treatment and alignment of the dental arches and the second is maintenance of the treatment results. of the treatment results. Orthodontic relapses are usually described as changes toward the Orthodontic relapses are usually described as changes toward the pretreatment status. These changes occur very fast if the teeth are not kept pretreatment status. These changes occur very fast if the teeth are not kept in their new position. That is the reason why, after orthodontic treatment, in their new position. That is the reason why, after orthodontic treatment, the result must be stabilized by some kind of retention device to prevent the result must be stabilized by some kind of retention device to prevent relapse. However, after this first period of remodeling of periodontal relapse. However, after this first period of remodeling of periodontal structures, comes the later period of changes. The problem is that these structures, comes the later period of changes. The problem is that these

13 13 changes generally cannot be distinguished from the normal aging process changes generally cannot be distinguished from the normal aging process that occurs, regardless of orthodontic treatment or not. that occurs, regardless of orthodontic treatment or not.

Anatomy of the Periodontium Anatomy of the Periodontium The periodontal space is occupied by cells, vessels, fluid and dento- The periodontal space is occupied by cells, vessels, fluid and dentoalveolar fibers, called the periodontal ligament (PDL). These periodontal alveolar fibers, called the periodontal ligament (PDL). These periodontal ligaments consist of collagen fibers that are arranged into fiber bundles. ligaments consist of collagen fibers that are arranged into fiber bundles. The portion of these fibers that is embedded into either cementum or bone The portion of these fibers that is embedded into either cementum or bone is called Sharpey's fibers. These fibers occasionally pass through the bone is called Sharpey's fibers. These fibers occasionally pass through the bone of the alveolar process to continue as principal fibers of an adjacent PDL. of the alveolar process to continue as principal fibers of an adjacent PDL. They may also run buccally and lingually to connect with the fibers of the They may also run buccally and lingually to connect with the fibers of the periosteum. Other fibers are: Circular fibers (runs around the tooth in the periosteum. Other fibers are: Circular fibers (runs around the tooth in the free gingiva), Dentogingival fibers, Dentoperiostal fibers, Alveologingival free gingiva), Dentogingival fibers, Dentoperiostal fibers, Alveologingival and Transseptal fibers17 ( Figure 1). and Transseptal fibers17 ( Figure 1).

14 14

Figure 1. Different fibers surrounding teeth. Periodontal ligament Figure 1. Different fibers surrounding teeth. Periodontal ligament (PDL), Circular fibers (CF), Dentogingival fibers (DGF), (PDL), Circular fibers (CF), Dentogingival fibers (DGF), Dentoperiostal fibers (DPF), Transseptal fibers (TSF) and Dentoperiostal fibers (DPF), Transseptal fibers (TSF) and Alveologingival fibers (AGF). Alveologingival fibers (AGF).

Biological and physiological role of periodontium and Biological and physiological role of periodontium and gingival tissue on relapse gingival tissue on relapse After orthodontic tooth movement, there is a need for remodeling of the After orthodontic tooth movement, there is a need for remodeling of the supporting tissues around the tooth, to prevent it returning to its former supporting tissues around the tooth, to prevent it returning to its former position.18-21 The periodontal ligaments and Sharpey's fibers act as an position.18-21 The periodontal ligaments and Sharpey's fibers act as an anchorage zone for new bone and new cementum. The middle and most anchorage zone for new bone and new cementum. The middle and most apical part of the root are more stable to relapse whereas the marginal third apical part of the root are more stable to relapse whereas the marginal third of the root is unstable.22 Reitan19 described the relapse that occurred after of the root is unstable.22 Reitan19 described the relapse that occurred after

15 15 tipping of the teeth in dogs without retention. He noticed that some relapse tipping of the teeth in dogs without retention. He noticed that some relapse already occurred after two hours, partly caused by the uprighting of the already occurred after two hours, partly caused by the uprighting of the tooth. Relapse continued to occur during the following four days. tooth. Relapse continued to occur during the following four days. Thereafter, this process stopped due to the hyalinized zone (cell free zone) Thereafter, this process stopped due to the hyalinized zone (cell free zone) on the tension side. A similar pattern was observed in children after tipping on the tension side. A similar pattern was observed in children after tipping teeth without subsequent retention.19 teeth without subsequent retention.19

The periodontal ligament remodels fast, but the gingival fibers have a slow The periodontal ligament remodels fast, but the gingival fibers have a slow turnover rate and take as long as 232 days to remodel after experimental turnover rate and take as long as 232 days to remodel after experimental tooth rotation.18 Transseptal and Dentoperiostal fibers of the gingiva, the tooth rotation.18 Transseptal and Dentoperiostal fibers of the gingiva, the fibers connecting thick maxillary frenulum to the alveolar process, also fibers connecting thick maxillary frenulum to the alveolar process, also need a very long period of remodeling and may be a source of relapse.23 need a very long period of remodeling and may be a source of relapse.23 Since the supra-alveolar fibers take a long time to remodel, some authors Since the supra-alveolar fibers take a long time to remodel, some authors suggest surgical circumferential incision of supra-alveolar structures suggest surgical circumferential incision of supra-alveolar structures (fibrotomy) that may prevent or reduce relapse after the experimental (fibrotomy) that may prevent or reduce relapse after the experimental rotation of teeth.24-27 rotation of teeth.24-27

The retention period is generally longer in adult patients, sometimes even The retention period is generally longer in adult patients, sometimes even permanent, due to thicker bundles of fibers and the decreased ability of the permanent, due to thicker bundles of fibers and the decreased ability of the periodontal and surrounding tissues to remodel after orthodontic tooth periodontal and surrounding tissues to remodel after orthodontic tooth movement.22,28 movement.22,28

When space is closed rapidly in extraction sites, there is a tendency toward When space is closed rapidly in extraction sites, there is a tendency toward reopening. It has been shown that compressed gingival tissue in an reopening. It has been shown that compressed gingival tissue in an extraction site may produce a gingival fold or invagination which is most extraction site may produce a gingival fold or invagination which is most frequently seen in premolar extraction sites.29 This hyperplasticity and frequently seen in premolar extraction sites.29 This hyperplasticity and excessive tissue may cause the reopening of space by pushing teeth apart excessive tissue may cause the reopening of space by pushing teeth apart (Figure 2). (Figure 2).

16 16

Figure 2. Gingival fold caused by rapid movement of teeth into an Figure 2. Gingival fold caused by rapid movement of teeth into an extraction site. extraction site.

According to Reitan19, there will be little or no relapse following According to Reitan19, there will be little or no relapse following orthodontic movement of an erupting tooth, since its supporting tissues are orthodontic movement of an erupting tooth, since its supporting tissues are in a proliferation stage as a result of the eruption process. New fibers will in a proliferation stage as a result of the eruption process. New fibers will be formed as the root develops, and these new fibers will assist in be formed as the root develops, and these new fibers will assist in maintaining the new tooth position. maintaining the new tooth position. It seems that the tongue puts more pressure on the teeth than the lips and It seems that the tongue puts more pressure on the teeth than the lips and chin.30,31 On the other hand, these forces are probably not of the magnitude chin.30,31 On the other hand, these forces are probably not of the magnitude to move well-supported teeth. When the bone level is reduced, due to to move well-supported teeth. When the bone level is reduced, due to periodontitis, some flaring of teeth to the buccal direction might be periodontitis, some flaring of teeth to the buccal direction might be observed. However, scientific ground for these hypotheses is very low. observed. However, scientific ground for these hypotheses is very low.

17 17 Dental arch changes Dental arch changes Henriksson et al.32 found changes instead of stability in the dental arch Henriksson et al.32 found changes instead of stability in the dental arch form in untreated subjects with normal occlusion, when passing from form in untreated subjects with normal occlusion, when passing from adolescence into adulthood. They found a significant increase of inter- adolescence into adulthood. They found a significant increase of inter- molar distance in the mandible in male subjects and a significantly more molar distance in the mandible in male subjects and a significantly more rounded lower dental arch form and reduction in arch depth in both sexes, rounded lower dental arch form and reduction in arch depth in both sexes, leading to increased irregularity of the lower incisors. leading to increased irregularity of the lower incisors. Thilander,33 in a longitudinal study of a population with normal occlusion Thilander,33 in a longitudinal study of a population with normal occlusion between the ages of 5 and 31 years, found anterior crowding, especially in between the ages of 5 and 31 years, found anterior crowding, especially in the mandible. The author explains it as the natural migration of teeth even the mandible. The author explains it as the natural migration of teeth even in the absence of third molars. in the absence of third molars. In a cast analysis study by Harris,34 arch size and form were measured in a In a cast analysis study by Harris,34 arch size and form were measured in a longitudinal survey of untreated adults, at 20 years of age and again at 55 longitudinal survey of untreated adults, at 20 years of age and again at 55 years of age. During this phase, arch lengths decreased significantly with years of age. During this phase, arch lengths decreased significantly with time. The arch widths increased, especially in the molar area, and even time. The arch widths increased, especially in the molar area, and even some small expansion occurred in the canine region. These slow changes some small expansion occurred in the canine region. These slow changes did not affect inter-arch relationship. did not affect inter-arch relationship. Bishara35 found the changes that took place from 25 to 45 years of age Bishara35 found the changes that took place from 25 to 45 years of age were, on average, of small magnitude but statistically significant (p < 0.05). were, on average, of small magnitude but statistically significant (p < 0.05). Both sexes experienced a significant increase in dental crowding in both Both sexes experienced a significant increase in dental crowding in both arches and it was more pronounced in the anterior segments and more arches and it was more pronounced in the anterior segments and more severe in the lower front. severe in the lower front. In another 20-year longitudinal study by Ward,36 changes in arch width of In another 20-year longitudinal study by Ward,36 changes in arch width of the maxillary and mandibular canine and molar in 60 subjects, older than the maxillary and mandibular canine and molar in 60 subjects, older than 20 years of age, were examined. Interestingly, approximately half of the 20 years of age, were examined. Interestingly, approximately half of the subjects were treated orthodontically. When comparing these two groups, subjects were treated orthodontically. When comparing these two groups,

18 18 the arch width and length decreased in both groups. Some intercanine the arch width and length decreased in both groups. Some intercanine expansion occurred in the upper arch but only in the treated group. expansion occurred in the upper arch but only in the treated group. The conclusion from these studies is that dental arches change over time The conclusion from these studies is that dental arches change over time and the natural path is the reduction of the arch length and migration of and the natural path is the reduction of the arch length and migration of teeth, leading to crowding in front regions, especially in the lower arch, teeth, leading to crowding in front regions, especially in the lower arch, until 55 years of age. Stability or very small changes were observed by until 55 years of age. Stability or very small changes were observed by Dager et al.,37 for subjects between 47-58 years of age. The occlusion Dager et al.,37 for subjects between 47-58 years of age. The occlusion follows these changes and the result seems to be “stable occlusion”. follows these changes and the result seems to be “stable occlusion”.

Relapse after orthodontic treatment of front teeth Relapse after orthodontic treatment of front teeth There is a large variation in treatment outcome due to the severity and type There is a large variation in treatment outcome due to the severity and type of malocclusion, treatment modality, patient cooperation, the growth and of malocclusion, treatment modality, patient cooperation, the growth and adaptation of soft and hard tissue.38 adaptation of soft and hard tissue.38 Relapse after orthodontic treatment is a well-known problem among Relapse after orthodontic treatment is a well-known problem among orthodontists. Surbeck et al.39 found that the pattern of pre-treatment orthodontists. Surbeck et al.39 found that the pattern of pre-treatment rotational displacement of maxillary anterior teeth had a tendency to repeat rotational displacement of maxillary anterior teeth had a tendency to repeat itself postretention. The authors also claimed that incomplete alignment itself postretention. The authors also claimed that incomplete alignment during treatment was a risk factor for relapse and suggested slight over during treatment was a risk factor for relapse and suggested slight over correction during active treatment of severely rotated teeth. Other studies correction during active treatment of severely rotated teeth. Other studies suggest fiberotomy and over correction to prevent the relapse of rotated suggest fiberotomy and over correction to prevent the relapse of rotated teeth.40,41 teeth.40,41 Several studies investigate the relapse of the lower front.42-51 The arch Several studies investigate the relapse of the lower front.42-51 The arch length decreases 52 and the inter-canine distance also decreases with time, length decreases 52 and the inter-canine distance also decreases with time, resulting in increasing irregularity in the lower front .53,54 Some authors resulting in increasing irregularity in the lower front .53,54 Some authors recommend having retainers in place permanently.42,51,55,56 One study recommend having retainers in place permanently.42,51,55,56 One study shows an acceptable effect of leaving a canine-to-canine retainer up to 20 shows an acceptable effect of leaving a canine-to-canine retainer up to 20

19 19 years. The author’s conclusion was that long-term retention with this kind years. The author’s conclusion was that long-term retention with this kind of device of mandibular incisor alignment is acceptable for most patients of device of mandibular incisor alignment is acceptable for most patients and quite compatible with periodontal health.57 and quite compatible with periodontal health.57 The present study focuses on upper front teeth. As mentioned before, The present study focuses on upper front teeth. As mentioned before, malalignment of maxillary front teeth is often the reason why patients seek malalignment of maxillary front teeth is often the reason why patients seek orthodontic treatment. There are different types of retention devices to keep orthodontic treatment. There are different types of retention devices to keep the upper front teeth stable after orthodontic treatment. the upper front teeth stable after orthodontic treatment.

Retention methods of upper front teeth Retention methods of upper front teeth A number of different removable or fixed retainers have been used to retain A number of different removable or fixed retainers have been used to retain upper front teeth after orthodontic treatment (Figures 3-8). The choice upper front teeth after orthodontic treatment (Figures 3-8). The choice depends on the initial malocclusion, expected growth and occlusal depends on the initial malocclusion, expected growth and occlusal development and the expected cooperation with use of retainers. Bonded development and the expected cooperation with use of retainers. Bonded retainers seem to be popular as they fairly effectively prevent tipping and retainers seem to be popular as they fairly effectively prevent tipping and rotation of the teeth. They are rather independent of cooperation and can be rotation of the teeth. They are rather independent of cooperation and can be used for long periods,39,54,58-60 although there are few studies on real long- used for long periods,39,54,58-60 although there are few studies on real long- term use. Some appliances, such as positioners and spring retainers, can be term use. Some appliances, such as positioners and spring retainers, can be used for minor tooth movements. Some, like the Jensen plate and the used for minor tooth movements. Some, like the Jensen plate and the Hawley retainer, are designed to allow vertical tooth movements. Hawley retainer, are designed to allow vertical tooth movements.

20 20

Figure 3. Positioner Figure 3. Positioner

Figure 4. Spring retainer Figure 4. Spring retainer

Figure 5. Essix 16-26 Figure 5. Essix 16-26

21 21

Figure 6. Hawley retainer Figure 6. Hawley retainer

Figure 7. Jensen Plate Figure 7. Jensen Plate

Figure 8. Bonded retainer Figure 8. Bonded retainer

22 22 AIMS AIMS

• The aims of the studies included in this thesis are to: • The aims of the studies included in this thesis are to: • Study the amount of relapse and long-term changes in alignment of the • Study the amount of relapse and long-term changes in alignment of the maxillary front teeth after retention with a bonded retainer. maxillary front teeth after retention with a bonded retainer. • Investigate the pattern of relapse regarding the type of movement after • Investigate the pattern of relapse regarding the type of movement after the correction of rotations and labial/lingual displacements. the correction of rotations and labial/lingual displacements. • Examine the effect of over correction of contact point displacement • Examine the effect of over correction of contact point displacement (CPD) in stability outcome. (CPD) in stability outcome. • Analyze the influence of expansion of the intercanine distance on • Analyze the influence of expansion of the intercanine distance on stability outcome. stability outcome.

23 23 MATERIALS AND METHODS MATERIALS AND METHODS

Materials Materials The study group consisted of 45 patients treated with fixed orthodontic The study group consisted of 45 patients treated with fixed orthodontic edgewise appliances. The patients were selected from the County edgewise appliances. The patients were selected from the County Orthodontic Clinic in Mariestad, Sweden, when their upper bonded Orthodontic Clinic in Mariestad, Sweden, when their upper bonded retainers were removed. retainers were removed. The wire used was 0.0195-inch Wildcat (GAC International Inc., Central The wire used was 0.0195-inch Wildcat (GAC International Inc., Central Islip, NY). Their mean age at the one year follow-up after removal of the Islip, NY). Their mean age at the one year follow-up after removal of the retainer was 18.8 years of age (range 15.8–21.5). retainer was 18.8 years of age (range 15.8–21.5). Extraction or nonextraction cases, with various diagnoses and where upper Extraction or nonextraction cases, with various diagnoses and where upper arches were retained with a bonded retainer only, were included. The mean arches were retained with a bonded retainer only, were included. The mean duration of the retention period was 33 months (range 23–48 months) duration of the retention period was 33 months (range 23–48 months) All six front permanent teeth had to be present before treatment and All six front permanent teeth had to be present before treatment and presenting irregularity. Spacing of the upper front teeth and treatments presenting irregularity. Spacing of the upper front teeth and treatments started as adults were excluded. started as adults were excluded. Study models before treatment (T1), after active treatment (T2), and one Study models before treatment (T1), after active treatment (T2), and one year out of upper retention (T3) had to be available. year out of upper retention (T3) had to be available. From the former group of 45 patients, a group of 27 patients were From the former group of 45 patients, a group of 27 patients were reexamined in the second study. Study models were collected at mean 7.6 reexamined in the second study. Study models were collected at mean 7.6 years (range 6.7–10.9 years) out of retention (T4). The mean age of the years (range 6.7–10.9 years) out of retention (T4). The mean age of the patients was 25.3 years of age (range 21.7–30.4 years of age). Considering patients was 25.3 years of age (range 21.7–30.4 years of age). Considering treatment and duration of retention and the mean irregularity index, this treatment and duration of retention and the mean irregularity index, this group was similar to the former group of 45. group was similar to the former group of 45.

24 24 Method for studying rotations and intercanine distance Method for studying rotations and intercanine distance In order to investigate individual rotational changes of the upper front teeth In order to investigate individual rotational changes of the upper front teeth in relation to the Raphe line and to measure the intercanine distance, a new in relation to the Raphe line and to measure the intercanine distance, a new modified method was developed and tested. modified method was developed and tested. Forty-five scanned pictures of study casts from 15 patients were randomly Forty-five scanned pictures of study casts from 15 patients were randomly selected. These pictures represented study casts taken before treatment selected. These pictures represented study casts taken before treatment (T1), at treatment end (T2) and one year postretention (T3). (T1), at treatment end (T2) and one year postretention (T3). An Agfa DuoScan F40 (Agfa-Gevaert N.V. Septestraat 27, B-2640 An Agfa DuoScan F40 (Agfa-Gevaert N.V. Septestraat 27, B-2640 Mortsel, Belgium) scanner was used to scan the casts. A computer Mortsel, Belgium) scanner was used to scan the casts. A computer program, the Scion Image Beta 4.02 for Windows, was used to measure program, the Scion Image Beta 4.02 for Windows, was used to measure angles and distances. It is a free program and can be downloaded from angles and distances. It is a free program and can be downloaded from http://www.scioncorp.com. http://www.scioncorp.com. To eliminate possible quality differences of the scanned area, casts were To eliminate possible quality differences of the scanned area, casts were placed on the upper third part of the glass and the scanned area of almost placed on the upper third part of the glass and the scanned area of almost the same size was used. The optimal quality for the pictures was set to 300 the same size was used. The optimal quality for the pictures was set to 300 DPI since the 2-3 times enlargement did not influence the quality other DPI since the 2-3 times enlargement did not influence the quality other than better details of the pictures, when plotting. than better details of the pictures, when plotting. Sixteen points were plotted in order from A to S. The letter (O) was not Sixteen points were plotted in order from A to S. The letter (O) was not used to eliminate the risk for mistaking it as zero. The positions of these 16 used to eliminate the risk for mistaking it as zero. The positions of these 16 points were oriented to the X- and Y-Axis of the scanned picture. These points were oriented to the X- and Y-Axis of the scanned picture. These points, two and two, make a line representing the incisor line of the tooth points, two and two, make a line representing the incisor line of the tooth (A-L), Raphe line (MN) and intercanine distance (RS). The rotations were (A-L), Raphe line (MN) and intercanine distance (RS). The rotations were measured as the angle between a line through two points on the incisal edge measured as the angle between a line through two points on the incisal edge of the teeth and the Raphe line. The intercanine distance was measured of the teeth and the Raphe line. The intercanine distance was measured between the cusp tips of the upper canines (Figure 9). between the cusp tips of the upper canines (Figure 9).

25 25

Figure 9. Reference points Figure 9. Reference points

For example, to measure the upper right cuspid’s angle to the Raphe line, For example, to measure the upper right cuspid’s angle to the Raphe line, the program constructed a line by connecting points A and B (canine line) the program constructed a line by connecting points A and B (canine line) and the points M and N (Raphe line) virtually. The following lines could be and the points M and N (Raphe line) virtually. The following lines could be achieved after plotting the points on the digitalized picture: AB= upper achieved after plotting the points on the digitalized picture: AB= upper right cuspid line, CD= upper right lateral incisor line, EF= upper right right cuspid line, CD= upper right lateral incisor line, EF= upper right central incisor line, GH= upper left central incisor line, IJ= upper left central incisor line, GH= upper left central incisor line, IJ= upper left lateral incisor line, KL= upper left cuspid line, MN = Raphe line and RS = lateral incisor line, KL= upper left cuspid line, MN = Raphe line and RS = intercanine distance (Figure 10). intercanine distance (Figure 10).

Figure 10. Showing the tooth angles on right side to Raphe line and Figure 10. Showing the tooth angles on right side to Raphe line and intercanine distance. intercanine distance.

26 26 All three scanned pictures (T1= before, T2= end of treatment, and T3= one All three scanned pictures (T1= before, T2= end of treatment, and T3= one year postretention) of each patient were opened simultaneously in separate year postretention) of each patient were opened simultaneously in separate windows and each point was marked as accurately as possible in all three windows and each point was marked as accurately as possible in all three images. Sixteen points (A-S) were marked on each picture (Figure 11 a-c). images. Sixteen points (A-S) were marked on each picture (Figure 11 a-c).

Figure 11 (a-c). T1, T2 and T3 of the same patient. Figure 11 (a-c). T1, T2 and T3 of the same patient.

The pictures, with all points marked, were saved. All three pictures were The pictures, with all points marked, were saved. All three pictures were reopened one by one in Scion image and the points were plotted for reopened one by one in Scion image and the points were plotted for measurements. The results were transferred and calculated in StatView ® measurements. The results were transferred and calculated in StatView ® version 4.51, Abacus Concepts. Inc. version 4.51, Abacus Concepts. Inc. Different formulas were used to calculate the correct angular measurements Different formulas were used to calculate the correct angular measurements and the intercanine distance. and the intercanine distance.

Method for studying contact point displacement (CPD) Method for studying contact point displacement (CPD) Labiolingual displacements of the anatomic contact points of all front teeth Labiolingual displacements of the anatomic contact points of all front teeth from the mesial of the right canine to the mesial of the left canine, were from the mesial of the right canine to the mesial of the left canine, were measured with a digital caliper on the casts from T1, T2, and T3, with 0.1 measured with a digital caliper on the casts from T1, T2, and T3, with 0.1 mm accuracy. CPDs less than 0.5 mm were judged to be zero. The mm accuracy. CPDs less than 0.5 mm were judged to be zero. The irregularity index, i.e. the sum of the five CPDs (Figure 12), was calculated irregularity index, i.e. the sum of the five CPDs (Figure 12), was calculated as described by Little.61 as described by Little.61

27 27

Figure 12. Irregularity index: The sum of five frontal contact Figure 12. Irregularity index: The sum of five frontal contact displacements in millimeters (A+B+C+D+E). displacements in millimeters (A+B+C+D+E).

Measurement errors Measurement errors To study measurement errors for rotational changes and intercanine To study measurement errors for rotational changes and intercanine distance, each scanned cast picture was measured twice with one month in- distance, each scanned cast picture was measured twice with one month in- between, with new points marked on fresh pictures. The error of the between, with new points marked on fresh pictures. The error of the method was calculated, based on Dahlberg’s formula,62 from the equation: method was calculated, based on Dahlberg’s formula,62 from the equation:

͸ D2 ͸ D2 ϭ ͱ ϭ ͱ Sx Sx 2N 2N Where D is the difference between duplicated measurements and N is the Where D is the difference between duplicated measurements and N is the number of double measurements. When measuring rotations to the Raphe number of double measurements. When measuring rotations to the Raphe line, the standard errors were 3.09° for canines and 2.78° for laterals and line, the standard errors were 3.09° for canines and 2.78° for laterals and 2.35° for centrals. The error of measuring intercanine distance was 1.12 2.35° for centrals. The error of measuring intercanine distance was 1.12 mm. The standard error of around 3° is, however, equal to the standard mm. The standard error of around 3° is, however, equal to the standard error for measuring many angles on a Cephalogram. error for measuring many angles on a Cephalogram. To calculate the measurement error for the contact point displacement, To calculate the measurement error for the contact point displacement, double measurements of 60 models, in 20 patients, were used. The double measurements of 60 models, in 20 patients, were used. The measurement error for CPD was 0.14 mm. measurement error for CPD was 0.14 mm.

28 28 Statistical analysis Statistical analysis

The SAS ® v8.2 program (SAS Institute Inc, Cary, NC) was used for all The SAS ® v8.2 program (SAS Institute Inc, Cary, NC) was used for all statistical analyses. For all statistical analyses, the statistical significance statistical analyses. For all statistical analyses, the statistical significance level was set to 5%. level was set to 5%.

Paper I Paper I Paired t-test was applied to test differences in the CPD, rotations, and the Paired t-test was applied to test differences in the CPD, rotations, and the intercanine distance between T1, T2, and T3. Pearson’s product-moment intercanine distance between T1, T2, and T3. Pearson’s product-moment correlation test was applied to test correlations between the CPD and correlation test was applied to test correlations between the CPD and rotations at T1 and changes during treatment and at follow-up. rotations at T1 and changes during treatment and at follow-up.

Paper II Paper II Pearson’s product-moment correlation coefficient was calculated to test for Pearson’s product-moment correlation coefficient was calculated to test for associations between irregularity index at T1/T3, T1/T4, and T3/T4. The associations between irregularity index at T1/T3, T1/T4, and T3/T4. The same analysis was also used to test for correlations between correction of same analysis was also used to test for correlations between correction of rotations/relapse of rotations and the change in mean CPD T2/T4 for the rotations/relapse of rotations and the change in mean CPD T2/T4 for the canine/lateral contact, the lateral/central contact, and the central/central canine/lateral contact, the lateral/central contact, and the central/central contact. contact.

29 29 RESULTS RESULTS

Contact point displacements Contact point displacements Before treatment (T1). The mean irregularity index at T1 was 10.1 (range Before treatment (T1). The mean irregularity index at T1 was 10.1 (range 3.0–29.9). The largest displacements were recorded between laterals and 3.0–29.9). The largest displacements were recorded between laterals and centrals followed by the displacement between laterals and canines, centrals followed by the displacement between laterals and canines, whereas the smallest deviations were found between the centrals. whereas the smallest deviations were found between the centrals. After treatment (T2). The mean irregularity index was 0.7 (range 0.0–2.1). After treatment (T2). The mean irregularity index was 0.7 (range 0.0–2.1). There was a significant difference in the index between T1 and T2 (P There was a significant difference in the index between T1 and T2 (P <.0001). Forty-three contacts were over corrected. Eighteen over <.0001). Forty-three contacts were over corrected. Eighteen over corrections were less than 0.5 mm (all were non measurable) and could corrections were less than 0.5 mm (all were non measurable) and could only be detected at close inspection. only be detected at close inspection. After retention (T3). The mean irregularity index at T3 was 1.4 (range 0– After retention (T3). The mean irregularity index at T3 was 1.4 (range 0– 5.1), i.e. 14% of the irregularity at T1. There was a significant difference in 5.1), i.e. 14% of the irregularity at T1. There was a significant difference in the index between T2 and T3 (P <.0001). the index between T2 and T3 (P <.0001). Results from the second study showed that there were no statistically Results from the second study showed that there were no statistically significant differences between the change in mean CPDs for the contacts significant differences between the change in mean CPDs for the contacts canines/laterals, laterals/centrals, or centrals/centrals. The mean irregularity canines/laterals, laterals/centrals, or centrals/centrals. The mean irregularity index for the 27 patients examined in the second study was 10.3 (range 3.7- index for the 27 patients examined in the second study was 10.3 (range 3.7- 29.9) at T1, 0.9 (range 0.0-2.1) at T2, 1.3 (range 0.0-3.5) at T3 and 2.0 29.9) at T1, 0.9 (range 0.0-2.1) at T2, 1.3 (range 0.0-3.5) at T3 and 2.0 (range 0.0-5.8) at T4. No correlations were found between the pretreatment (range 0.0-5.8) at T4. No correlations were found between the pretreatment and postretention irregularity T1/T3 and T1/T4. There was a significant and postretention irregularity T1/T3 and T1/T4. There was a significant association between the irregularity index at T3 and T4 (R = 0.938, P < association between the irregularity index at T3 and T4 (R = 0.938, P < .0001), (Figure 13). .0001), (Figure 13).

30 30

Figure 13. Contact Point Displacements at T1, T2, T3 and T4. Figure 13. Contact Point Displacements at T1, T2, T3 and T4.

Twenty over corrected contacts were noted. Of the 20 over corrected CPDs, Twenty over corrected contacts were noted. Of the 20 over corrected CPDs, 10 showed perfect contacts at T4 and four were to some degree still over 10 showed perfect contacts at T4 and four were to some degree still over corrected. Six contacts had relapsed 0.8–2.1 mm (Figure 14). corrected. Six contacts had relapsed 0.8–2.1 mm (Figure 14).

20 over corrected contacts at T2, T3, T4 20 over corrected contacts at T2, T3, T4

4 4

3.7 3.7

3 3

2.7 2.7

2 2 V"4 V"4 /2.7 V"5 /2.7 V"5 /3 V6 /3 V6

/3.7 /3.7 se (-), over correction (+) mm correction(-), over se (+) mm correction(-), over se /4 /4 relapse (-), over correction (+) mm correction (-), over relapse (+) mm correction (-), over relapse /4.7 /4.7

Figure 14. Twenty over corrected contacts at T2, T3 and T4. Figure 14. Twenty over corrected contacts at T2, T3 and T4.

31 31 Rotations Rotations There was a significant correlation between the amount of rotational There was a significant correlation between the amount of rotational change (for all six teeth) due to treatment and relapse (P< .0001). However, change (for all six teeth) due to treatment and relapse (P< .0001). However, when looking at each tooth group, centrals (P< .0130) and laterals (P< when looking at each tooth group, centrals (P< .0130) and laterals (P< .0001) showed significant correlations but not the canines (P < .0622). .0001) showed significant correlations but not the canines (P < .0622). A total of 40 rotated teeth in 21 patients were corrected more than 20° A total of 40 rotated teeth in 21 patients were corrected more than 20° during treatment (range 20.3°–51.9°). Mean relapse during the first year during treatment (range 20.3°–51.9°). Mean relapse during the first year postretention (T2–T3) was 6.7° (range 0.0°–14.7°). Seven years postretention (T2–T3) was 6.7° (range 0.0°–14.7°). Seven years postretention (T2–T4), the mean relapse was 8.2° (range 0.0°–19.3°). postretention (T2–T4), the mean relapse was 8.2° (range 0.0°–19.3°). Most of the changes were seen at one year postretention (T3). Positive Most of the changes were seen at one year postretention (T3). Positive correlation between rotational correction in treatment and long-term relapse correlation between rotational correction in treatment and long-term relapse was statistically significant for centrals (P = .0004), laterals (P = .0007) and was statistically significant for centrals (P = .0004), laterals (P = .0007) and the canines (P = .0056). the canines (P = .0056).

Intercanine distance Intercanine distance In 14 patients, the intercanine distance was expanded equal to or more than In 14 patients, the intercanine distance was expanded equal to or more than 1.5 mm from T1-T2 (range 1.5–6.4). Four of these 14 patients showed a 1.5 mm from T1-T2 (range 1.5–6.4). Four of these 14 patients showed a reduction of the intercanine width at T3 of 1 mm or more (range 1.0–2.3). reduction of the intercanine width at T3 of 1 mm or more (range 1.0–2.3). Five of nine individuals followed to T4, showed a relapse of 1 mm or more Five of nine individuals followed to T4, showed a relapse of 1 mm or more (range 1.1–2.3) of the intercanine distance. Among the patients without (range 1.1–2.3) of the intercanine distance. Among the patients without increased intercanine distance during treatment, three showed a decreased increased intercanine distance during treatment, three showed a decreased intercanine distance of 1.5–2.3 mm at T4. intercanine distance of 1.5–2.3 mm at T4.

32 32 DISCUSSION DISCUSSION

When measuring the contact point displacement, a calliper is a common When measuring the contact point displacement, a calliper is a common tool, but other methods such as a reflex microscope have also been used.63 tool, but other methods such as a reflex microscope have also been used.63 However, to measure rotations on a study model is a more challenging task However, to measure rotations on a study model is a more challenging task and some different methods have been described. and some different methods have been described. In general, two different methods have been used earlier to identify and In general, two different methods have been used earlier to identify and compare changes after orthodontic treatment. The first method measures compare changes after orthodontic treatment. The first method measures plain rotations of the upper six front teeth to the Raphe line on a photocopy plain rotations of the upper six front teeth to the Raphe line on a photocopy of casts.64-66 With this method, difficulty in locating the Raphe line equally of casts.64-66 With this method, difficulty in locating the Raphe line equally on the pretreatment, post treatment and postretention study models causes on the pretreatment, post treatment and postretention study models causes measurement errors. The variation in the quality of the plaster casts is measurement errors. The variation in the quality of the plaster casts is another factor that may increase the measurement error. another factor that may increase the measurement error. The second method is based on the arch form and its changes during and The second method is based on the arch form and its changes during and after treatment.32,39,47,67,68 The second method does not distinguish changes after treatment.32,39,47,67,68 The second method does not distinguish changes of each individual tooth because it is aimed to investigate the arch shape of each individual tooth because it is aimed to investigate the arch shape and form and its changes over time. Rotations of teeth are measured and form and its changes over time. Rotations of teeth are measured relative to a computer generated arch form in this method. Surbeck et al.39 relative to a computer generated arch form in this method. Surbeck et al.39 stated that their method might indicate CPD and incisor rotations even in a stated that their method might indicate CPD and incisor rotations even in a group selected for perfect alignment. This shows that a computer generated group selected for perfect alignment. This shows that a computer generated arch form may not represent the actual dental arch, and teeth may be arch form may not represent the actual dental arch, and teeth may be rotated, but the computer generated arch form does not show it. rotated, but the computer generated arch form does not show it. It was considered to be of interest to investigate the individual tooth and its It was considered to be of interest to investigate the individual tooth and its rotational change to previous position and to distinguish between rotation rotational change to previous position and to distinguish between rotation and contact point displacement. Therefore, the first method was chosen but and contact point displacement. Therefore, the first method was chosen but instead of doing measurements manually on a photocopy paper, it was instead of doing measurements manually on a photocopy paper, it was

33 33 decided to produce and test a new modified and computer-aided method, to decided to produce and test a new modified and computer-aided method, to study rotational changes of six upper front teeth to the Raphe line. study rotational changes of six upper front teeth to the Raphe line. In the first study, 89% of the patients had a score of less than 3 mm for the In the first study, 89% of the patients had a score of less than 3 mm for the maxillary irregularity index, one year out of retention. The change from a maxillary irregularity index, one year out of retention. The change from a mean irregularity index of 0.7 mm after treatment to 1.4 mm after retention mean irregularity index of 0.7 mm after treatment to 1.4 mm after retention can be regarded as a minor relapse compared with the original irregularity can be regarded as a minor relapse compared with the original irregularity index of 10.1 mm. The irregularity one year after retention was 14% of the index of 10.1 mm. The irregularity one year after retention was 14% of the value before treatment. In comparison with other studies using Hawley value before treatment. In comparison with other studies using Hawley retainers,27,46,69,70 these results seem to be favorable; i.e. less postretention retainers,27,46,69,70 these results seem to be favorable; i.e. less postretention changes were observed in this study. No correlations were observed changes were observed in this study. No correlations were observed between the severity of pretreatment irregularity and the amount of relapse. between the severity of pretreatment irregularity and the amount of relapse. This means that severe cases did not relapse more compared to the cases This means that severe cases did not relapse more compared to the cases with less initial irregularity one year postretention. with less initial irregularity one year postretention. Since the follow-up period was only one year, the results were considered Since the follow-up period was only one year, the results were considered as short-term. A recall visit one year out of retention was, in most cases, the as short-term. A recall visit one year out of retention was, in most cases, the patient’s last visit to the orthodontist. However, small contact patient’s last visit to the orthodontist. However, small contact displacements one year after retention may be potential starting points for displacements one year after retention may be potential starting points for increasing irregularity. It was of interest to learn if this was the case in the increasing irregularity. It was of interest to learn if this was the case in the second study. second study. At the long-term follow-up in the second study, the irregularity index of the At the long-term follow-up in the second study, the irregularity index of the maxillary front teeth increased among patients. But still 70 percent of the maxillary front teeth increased among patients. But still 70 percent of the patients had an irregularity index of less than 3 mm. A weakness in this patients had an irregularity index of less than 3 mm. A weakness in this material is the relatively small number of patients (n= 27) with records one material is the relatively small number of patients (n= 27) with records one and seven years postretention. But the 27 patients that were examined long- and seven years postretention. But the 27 patients that were examined long- term were, in all aspects, similar to the larger group of 45 subjects (initial term were, in all aspects, similar to the larger group of 45 subjects (initial irregularity, treatment, duration of retention). irregularity, treatment, duration of retention). A strength with this study is that the original 45 patients reported in the one A strength with this study is that the original 45 patients reported in the one year study were selected at the appointment when the retainer was year study were selected at the appointment when the retainer was

34 34 removed. Most other studies are based on retrospective removed. Most other studies are based on retrospective materials27,38,39,46,66,69,71 selected from larger collections. All of the patients materials27,38,39,46,66,69,71 selected from larger collections. All of the patients in this study had the same method of retention, i.e. upper bonded retainer, in this study had the same method of retention, i.e. upper bonded retainer, and the length of the retention period and the postretention period is and the length of the retention period and the postretention period is specified. These variables have a wider range in many studies or are not specified. These variables have a wider range in many studies or are not reported at all.38,39,46,66,69,71,72 reported at all.38,39,46,66,69,71,72 Most of the patients, who showed minor irregularities one year Most of the patients, who showed minor irregularities one year postretention, were more irregular at the long-term follow-up, resulting in postretention, were more irregular at the long-term follow-up, resulting in that 14% of the contacts were displaced more than 1 mm, maximum 2.2 that 14% of the contacts were displaced more than 1 mm, maximum 2.2 mm. There was a strong correlation between irregularity one year mm. There was a strong correlation between irregularity one year postretention and long-term seven years postretention, but the findings of postretention and long-term seven years postretention, but the findings of Surbeck et al.39, that pretreatment irregularity is a significant risk indicator Surbeck et al.39, that pretreatment irregularity is a significant risk indicator for postretention relapse, could not be confirmed. However, half of the for postretention relapse, could not be confirmed. However, half of the group of 27 patients did not change at all and they were stable during the group of 27 patients did not change at all and they were stable during the whole postretention period. Concerning corrected rotations, almost all whole postretention period. Concerning corrected rotations, almost all relapse was seen one year postretention with very small further changes. relapse was seen one year postretention with very small further changes. The contact relationship between laterals and centrals showed the largest The contact relationship between laterals and centrals showed the largest CPD at T1, which is in accordance with the earlier findings.69 Regarding CPD at T1, which is in accordance with the earlier findings.69 Regarding alignment of the maxillary anterior teeth, the contact relationship between alignment of the maxillary anterior teeth, the contact relationship between the lateral and central seems to be most critical. The correction of a bodily the lateral and central seems to be most critical. The correction of a bodily displaced tooth, often laterals, includes selective root torque to minimize displaced tooth, often laterals, includes selective root torque to minimize the relapse tendency. Otherwise, only the crown is tipped buccally and the the relapse tendency. Otherwise, only the crown is tipped buccally and the root is still on the palatal side. root is still on the palatal side. The laterals showed more rotational mean relapse than centrals and The laterals showed more rotational mean relapse than centrals and canines, and of the 12 rotations that relapsed more than 10°, eight were canines, and of the 12 rotations that relapsed more than 10°, eight were laterals. The data confirmed the findings of Surbeck et al.39, that most laterals. The data confirmed the findings of Surbeck et al.39, that most rotational relapses of the maxillary incisors are approximately 10°. Half of rotational relapses of the maxillary incisors are approximately 10°. Half of the over corrected contacts were nicely aligned at T4. The over corrections the over corrected contacts were nicely aligned at T4. The over corrections

35 35 that were noticed to have relapsed, one year postretention, had a tendency that were noticed to have relapsed, one year postretention, had a tendency of continued relapse. of continued relapse. The irregularity index is not always reflecting the esthetic impression of the The irregularity index is not always reflecting the esthetic impression of the teeth; evenly distributed small CPDs are probably better than one or two teeth; evenly distributed small CPDs are probably better than one or two major displaced contacts with the lateral/central contact often being the major displaced contacts with the lateral/central contact often being the most critical. The experience is that rotations of up to 10° are not visible. A most critical. The experience is that rotations of up to 10° are not visible. A relapse in the range of 15° to 20° can be detected at close examination. Of relapse in the range of 15° to 20° can be detected at close examination. Of the 40 severe rotations in this study, 15% relapsed within that range (15.6°– the 40 severe rotations in this study, 15% relapsed within that range (15.6°– 19.3°). 19.3°). From an esthetic point of view, a slightly disto-buccally rotated upper From an esthetic point of view, a slightly disto-buccally rotated upper canine is not likely to be disturbing due to the curved buccal surface. A canine is not likely to be disturbing due to the curved buccal surface. A rotation that causes a broken contact may be more displeasing. The clinical rotation that causes a broken contact may be more displeasing. The clinical impression is that the contact between lateral and central is the most critical impression is that the contact between lateral and central is the most critical concerning correction and stability. If, after a 3-year period of retention, a concerning correction and stability. If, after a 3-year period of retention, a decision is made to use permanent retention of the maxillary front teeth, a decision is made to use permanent retention of the maxillary front teeth, a retainer bonded to only the incisors seems to be a relevant choice. retainer bonded to only the incisors seems to be a relevant choice. Bond failures for the 306 teeth with bonded retainer were recorded in six Bond failures for the 306 teeth with bonded retainer were recorded in six teeth in five patients during the retention period. There are different reasons teeth in five patients during the retention period. There are different reasons mentioned in the literature affecting the results such as material, dimension mentioned in the literature affecting the results such as material, dimension and shape of the retainer, method, operator skills, patient habits, patient and shape of the retainer, method, operator skills, patient habits, patient intercuspidation and so on.58-60,73-77 In this study, most patients achieved a intercuspidation and so on.58-60,73-77 In this study, most patients achieved a proper overbite with almost no interferences. In patients with short upper proper overbite with almost no interferences. In patients with short upper clinical crowns, the wire was placed more cervically. All the patients in this clinical crowns, the wire was placed more cervically. All the patients in this study had the same operator. study had the same operator. The failure rate of upper bonded retained teeth (2%) in the present studies The failure rate of upper bonded retained teeth (2%) in the present studies is consistent with the findings of Zachrisson58 and must be considered very is consistent with the findings of Zachrisson58 and must be considered very good since some studies show that bond failure is higher in the upper front good since some studies show that bond failure is higher in the upper front than the lower front.75,78 In addition, four of six retainer failures in this than the lower front.75,78 In addition, four of six retainer failures in this

36 36 study affected premolars (48 premolars were involved), which are study affected premolars (48 premolars were involved), which are considered to have even higher failure rates. considered to have even higher failure rates.

Only a few individuals exhibited an increased intercanine width during Only a few individuals exhibited an increased intercanine width during treatment. No obvious changes could be recorded in the intercanine treatment. No obvious changes could be recorded in the intercanine distance between T2 and T3. Since four subjects showed a decreased width, distance between T2 and T3. Since four subjects showed a decreased width, no safe conclusions can be drawn from these findings. no safe conclusions can be drawn from these findings. Fiberotomy was performed on only nine incisors. Their degree of relapse Fiberotomy was performed on only nine incisors. Their degree of relapse was not different from the remaining 46 teeth corrected more than 20°. was not different from the remaining 46 teeth corrected more than 20°. Studies that used Hawley retainers as retention found less relapse in a Studies that used Hawley retainers as retention found less relapse in a group with fiberotomies as compared with a group without.24 group with fiberotomies as compared with a group without.24 Of the 25 measurable over corrections at T2, 14 had returned to zero CPD Of the 25 measurable over corrections at T2, 14 had returned to zero CPD at T3. It is not known if the four over corrections that relapsed toward the at T3. It is not known if the four over corrections that relapsed toward the original position (T1) would have been of a different magnitude without original position (T1) would have been of a different magnitude without over correction. The seven remaining over corrections were so small (0.5– over correction. The seven remaining over corrections were so small (0.5– 1.1 mm) that they probably did not cause the patients any dissatisfaction. 1.1 mm) that they probably did not cause the patients any dissatisfaction. It can be concluded that over corrections should be small since there is a It can be concluded that over corrections should be small since there is a risk that some do not rebound to zero CPD. It is uncertain how much the risk that some do not rebound to zero CPD. It is uncertain how much the result can be improved by over correction. result can be improved by over correction. Using implants as reference points could be regarded as the most stable and Using implants as reference points could be regarded as the most stable and reliable method when measuring rotations. As they can only be used in reliable method when measuring rotations. As they can only be used in specific situations, the Raphe line can be considered relatively easy to use specific situations, the Raphe line can be considered relatively easy to use as reference to measure rotations of the upper front teeth. as reference to measure rotations of the upper front teeth. In recent years, laser scanning of study models has given us a more In recent years, laser scanning of study models has given us a more accurate picture of changes during treatment and postretention. However, it accurate picture of changes during treatment and postretention. However, it is still expensive to acquire these machines, but they may have a future for is still expensive to acquire these machines, but they may have a future for the evaluation of the treatment and relapse after orthodontic treatment. the evaluation of the treatment and relapse after orthodontic treatment.

37 37 CONCLUSIONS CONCLUSIONS

• Minor or no relapse in short-term follow-up (1 year) was noted in the • Minor or no relapse in short-term follow-up (1 year) was noted in the maxillary front after correction of irregularity and a two to four year maxillary front after correction of irregularity and a two to four year period of bonded retention. Further, small relapse occurred long-term period of bonded retention. Further, small relapse occurred long-term i.e. at mean seven years postretention. i.e. at mean seven years postretention. • No significant relation was found between the amount of correction of • No significant relation was found between the amount of correction of contact point displacement and magnitude of relapse neither in one, nor contact point displacement and magnitude of relapse neither in one, nor seven years postretention. seven years postretention. • There was a strong correlation between irregularity one and seven years • There was a strong correlation between irregularity one and seven years postretention. Stable cases one year postretention are stable in the long- postretention. Stable cases one year postretention are stable in the long- term and cases with small changes one year postretention tend to term and cases with small changes one year postretention tend to deteriorate with time. deteriorate with time. • Most of the rotational relapse was seen one year postretention with • Most of the rotational relapse was seen one year postretention with small changes long-term. small changes long-term. • There was a significant positive correlation between the amount of • There was a significant positive correlation between the amount of correction of incisor rotation and the magnitude of relapse. correction of incisor rotation and the magnitude of relapse. • Of the over corrected contacts, only 50 percent returned to perfect • Of the over corrected contacts, only 50 percent returned to perfect alignment. alignment. • Laterals are more prone to relapse. If, after a three year period of • Laterals are more prone to relapse. If, after a three year period of retention, a decision is made to use permanent retention of the maxillary retention, a decision is made to use permanent retention of the maxillary front teeth, a retainer bonded to only the incisors seems to be a relevant front teeth, a retainer bonded to only the incisors seems to be a relevant choice. choice.

38 38 ACKNOWLEDGMENTS ACKNOWLEDGMENTS

I wish to express my deepest and sincerest thanks to everyone who has I wish to express my deepest and sincerest thanks to everyone who has helped and supported me during these years with my project. Especially, I helped and supported me during these years with my project. Especially, I would like to thank: would like to thank: Professor Bengt Mohlin, my supervisor and co-author. Thank you for your Professor Bengt Mohlin, my supervisor and co-author. Thank you for your kindness and knowledge in the subject. I have learned much during these kindness and knowledge in the subject. I have learned much during these years, talking to you and learning how to be an open-minded researcher and years, talking to you and learning how to be an open-minded researcher and human being. human being. Associate professor Heidrun Kjellberg, my supervisor and co-author. Associate professor Heidrun Kjellberg, my supervisor and co-author. Thank you for your speed on returning manuscripts, all your wise Thank you for your speed on returning manuscripts, all your wise comments and your sharp eyes. comments and your sharp eyes. Dr. Anders Andrén as a co-author of both papers. I am grateful that we Dr. Anders Andrén as a co-author of both papers. I am grateful that we could use your data material for this thesis. It has been a pleasure to know could use your data material for this thesis. It has been a pleasure to know you and work with you. you and work with you. The Orthodontic Department in Växjö, Kronoberg Region, for all the The Orthodontic Department in Växjö, Kronoberg Region, for all the support during these years and encouraging me to finish my project. support during these years and encouraging me to finish my project. Odont Dr. Tailun He, for all his help with the mathematical formulas to Odont Dr. Tailun He, for all his help with the mathematical formulas to calculate angles in the computer program. calculate angles in the computer program.

Sandra Ståhlberg, for revision of the English text. Sandra Ståhlberg, for revision of the English text. And finally, I am deeply grateful to my wife Peggy and my daughters And finally, I am deeply grateful to my wife Peggy and my daughters Jasmin and Shirin for their understanding and acceptance of my Jasmin and Shirin for their understanding and acceptance of my involvement in this project. involvement in this project.

These studies were supported financially by the following grants: Public These studies were supported financially by the following grants: Public Dental Health Service, and FOU centre in both the Kronoberg and Västra Dental Health Service, and FOU centre in both the Kronoberg and Västra

Götalands Region. Götalands Region.

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43 43 63. Atack N, Harradine N, Sandy JR, Ireland AJ. Which way forward? 63. Atack N, Harradine N, Sandy JR, Ireland AJ. Which way forward? Fixed or removable lower retainers. Angle Orthod 2007;77:954-959. Fixed or removable lower retainers. Angle Orthod 2007;77:954-959. 64. Sanin C, Hixon EH. Axial rotations of maxillary permanent incisors. 64. Sanin C, Hixon EH. Axial rotations of maxillary permanent incisors. Angle Orthod 1968;38:269-283. Angle Orthod 1968;38:269-283. 65. Swanson WD, Riedel RA, D'Anna JA. Postretention study: incidence 65. Swanson WD, Riedel RA, D'Anna JA. Postretention study: incidence and stability of rotated teeth in humans. Angle Orthod 1975;45:198-203. and stability of rotated teeth in humans. Angle Orthod 1975;45:198-203. 66. Jones ML. The Barry Project--a further assessment of occlusal 66. Jones ML. The Barry Project--a further assessment of occlusal treatment change in a consecutive sample: crowding and arch dimensions. treatment change in a consecutive sample: crowding and arch dimensions. Br J Orthod 1990;17:269-285. Br J Orthod 1990;17:269-285. 67. Sampson PD. Dental arch shape: a statistical analysis using conic 67. Sampson PD. Dental arch shape: a statistical analysis using conic sections. Am J Orthod 1981;79:535-548. sections. Am J Orthod 1981;79:535-548. 68. Davis LM, BeGole EA. Evaluation of orthodontic relapse using the 68. Davis LM, BeGole EA. Evaluation of orthodontic relapse using the cubic spline function. Am J Orthod Dentofacial Orthop 1998;113:300-306. cubic spline function. Am J Orthod Dentofacial Orthop 1998;113:300-306. 69. Vaden JL, Harris EF, Gardner RL. Relapse revisited. Am J Orthod 69. Vaden JL, Harris EF, Gardner RL. Relapse revisited. Am J Orthod Dentofacial Orthop 1997;111:543-553. Dentofacial Orthop 1997;111:543-553. 70. Huang L, Artun J. Is the postretention relapse of maxillary and 70. Huang L, Artun J. Is the postretention relapse of maxillary and mandibular incisor alignment related? Am J Orthod Dentofacial Orthop mandibular incisor alignment related? Am J Orthod Dentofacial Orthop 2001;120:9-19. 2001;120:9-19. 71. Sadowsky C, Sakols EI. Long-term assessment of orthodontic relapse. 71. Sadowsky C, Sakols EI. Long-term assessment of orthodontic relapse. Am J Orthod 1982;82:456-463. Am J Orthod 1982;82:456-463. 72. Boley JC, Mark JA, Sachdeva RC, Buschang PH. Long-term stability 72. Boley JC, Mark JA, Sachdeva RC, Buschang PH. Long-term stability of Class I premolar extraction treatment. Am J Orthod Dentofacial Orthop of Class I premolar extraction treatment. Am J Orthod Dentofacial Orthop 2003;124:277-287. 2003;124:277-287. 73. Zachrisson BJ. A posttreatment evaluation of direct bonding in 73. Zachrisson BJ. A posttreatment evaluation of direct bonding in orthodontics. Am J Orthod 1977;71:173-189. orthodontics. Am J Orthod 1977;71:173-189. 74. Zachrisson BU. The bonded lingual retainer and multiple spacing of 74. Zachrisson BU. The bonded lingual retainer and multiple spacing of anterior teeth. Swed Dent J Suppl 1982;15:247-255. anterior teeth. Swed Dent J Suppl 1982;15:247-255. 75. Dahl EH, Zachrisson BU. Long-term experience with direct-bonded 75. Dahl EH, Zachrisson BU. Long-term experience with direct-bonded lingual retainers. J Clin Orthod 1991;25:619-630. lingual retainers. J Clin Orthod 1991;25:619-630. 76. Paulson RC. A functional rationale for routine maxillary bonded 76. Paulson RC. A functional rationale for routine maxillary bonded retention. Angle Orthod 1992;62:223-226. retention. Angle Orthod 1992;62:223-226. 77. Zachrisson BJ. Third-generation mandibular bonded lingual 3-3 77. Zachrisson BJ. Third-generation mandibular bonded lingual 3-3 retainer. J Clin Orthod 1995;29:39-48. retainer. J Clin Orthod 1995;29:39-48. 78. Lumsden KW, Saidler G, McColl JH. Breakage incidence with direct- 78. Lumsden KW, Saidler G, McColl JH. Breakage incidence with direct- bonded lingual retainers. Br J Orthod 1999;26:191-194. bonded lingual retainers. Br J Orthod 1999;26:191-194.

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